“Soon we were timing the fall of scoring markers from our balloons. We discovered that a standard marker fell about 3,000 feet per minute. I then built the first drop sight– two pieces of rigid quarter-inch plastic sheet hinged together. One piece included level sight tubes so it could be kept level. The other could be set to a downward angle according to a scale calibrated in miles per hour of average wind speed. In flight I would set the wind speed on the scale and then sight along the tilted piece until the target was in line with it, at which point I would release the drop marker. This worked, but the device was big and clumsy. Not long after, David designed and built two beautiful pistol-shaped, varnished hardwood drop sights with level sight tubes and wind speed scales. I made a padded “holster” for mine, which I tied into the inside of my basket, ready to use. I used this drop sight for the rest of the years I competed. No single tool wins balloon competitions, but I am sure this drop sight got me points when I needed to use it.”Comstock, Bruce (2013-10-23). A Life in the Air (Kindle Locations 1189-1195). Willow Press.

“I just studied my archives and found a marker drop altitude&time table written by myself. It is based on marker falling speed of 3000 ft/min. Time of writing: 1985-1987.